1. Field
The present invention relates to a liquid crystal display device, and more particularly, to a transflective liquid crystal display device having high utilization efficiency for light and a fabricating method thereof.
2. Discussion of the Related Art
Generally, transflective liquid crystal display (LCD) devices function as both transmissive and reflective LCD devices. Because transflective LCD devices can use both a backlight and natural or artificial ambient light, the transflective LCD devices may be used in more circumstances, and power consumption of transflective LCD devices may be reduced.
FIG. 1 is an exploded perspective view of an LCD device according to the related art. As shown in FIG. 1, a liquid crystal display (LCD) device 10 has an upper substrate 12 having a black matrix 17, a color filter layer 16 including sub-color filters and a common electrode 13 on the color filter layer 16, and a lower substrate 14 having a thin film transistor (TFT) T and a pixel electrode 20 connected to the TFT T. A liquid crystal layer 18 is interposed between the common electrode 13 and the pixel electrode 20. The lower substrate 14 is referred to as an array substrate because array lines including a gate line 25 and a data line 27 are formed thereon. The gate line 25 and the data line 27 cross each other forming a matrix, and the TFT T is connected to the gate line 25 and the data line 27. The gate line 25 and the data line 27 define a pixel region P by crossing each other, and the TFT T is formed near a crossing portion of the gate line 25 and the data line 27. The pixel electrode 20 is formed of a transparent conductive material such as indium-tin-oxide (ITO) and indium-zinc-oxide (IZO) in the pixel region P. The upper substrate 12 is referred to as a color filter substrate because the color filter layer 16 is formed thereon.
A reflective layer 21 of a reflective material such as aluminum (Al) or Al alloy is formed in the pixel region P. However, when the reflective layer 21 is connected to the pixel electrode 20, the reflective layer 21 can act as an electrode. The reflective layer 21 has a transmittance hole H so that the pixel region P is divided into a reflective portion RP and a transmissive portion TP. The transmissive portion TP corresponds to the transmissive hole H and the reflective portion RP corresponds to the other portions of the reflective layer 21.
However, because the transflective LCD device is manufactured to selectively use a reflective mode or a transmissive mode, utilization efficiency for light is relatively low. Particularly, when the transflective LCD device is used as the reflective mode, it depends on natural light. Therefore, the utilization efficiency is low in comparison with the transmissive mode. As a result, interchanging the reflective mode with the transmissive mode causes a brightness difference.
To solve these problems, an uneven reflective layer is formed on the reflective portion to induce an irregular reflection by minimizing incident light specularly-reflected from outside and to improve the entire brightness of the reflective mode and transmissive mode according to the related art.
Hereinafter, the transflective LCD device having the uneven reflective layer according to the related art will be explained referring to FIG. 2.
FIG. 2 is a schematic plan view showing one pixel region for a transflective LCD device having an uneven reflective layer according to the related art.
In FIG. 2, a gate line 34 is formed on a substrate 30 along a first direction, and a data line 46 crosses the gate line 34 to define a pixel region P.
A thin film transistor T is formed near a crossing of the gate line 34 and the data line 46. A gate electrode 32, a semiconductor layer 41, source and drain electrodes 42 and 44 constitute the thin film transistor T.
A pixel electrode 60 of a transparent conductive material is formed in the pixel region P and is connected to the thin film transistor T. A reflective layer 64 having a plurality of unevenesses 52 is formed in the pixel region P and has a transmissive hole 58 that exposes the central portion of the pixel electrode 60.
The pixel region P includes a transmissive portion TP in the transmissive hole 58 and a reflective portion RP in a portion of the reflective layer 21 except a portion of the transmissive hole 58.
That is to say, the pixel electrode 60 acts as a driving electrode of the liquid crystal layer 18 (of FIG. 1) with the common electrode 13 (of FIG. 1). On the other hand, the reflective layer 64 (or reflective electrode) mainly acts as a reflective means. Therefore, the uneven patterns increase reflectance of a surface of the reflective layer.
Next, it will be explained about the fabricating method for the transflective LCD device having the uneven reflective layer according to the related art.
FIGS. 3A to 3G are schematic cross sectional views taken along lines III-III of FIG. 2, which shows a fabricating process for a transflective LCD device according to the related art.
In FIG. 3A, a switching region S, a transmissive portion TP, and a reflective portion RP in periphery of the transmissive portion TP are defined in a substrate 30. The transmissive and reflective portion TP and RP constitute a pixel region P.
A gate electrode 32 is formed on the substrate 30 in the switching region S. For example, the gate electrode 32 is formed as a single layer or a double layer. When the gate electrode 32 is a single layer, it is selected from one of aluminum (Al), Al alloy, tungsten (W), chromium (Cr) and molybdenum (Mo). Meanwhile, when the gate electrode 32 is a double layer, the gate electrode 32 is selected from one of Al/Cr and Al/Mo.
In FIG. 3B, a gate insulating layer 36 is formed of inorganic insulating materials over an entire surface of the substrate 30 having the gate electrode 32, and an active layer 38 and an ohmic contact layer 40 are sequentially formed on the gate insulating layer 36. The active layer 38 and the ohmic contact layer 40 are made of intrinsic amorphous silicon and the doped amorphous silicon, respectively. The active layer 38 and the ohmic contact layer 40 constitute a semiconductor layer 41.
In FIG. 3C, source and drain electrodes 42 and 44 are formed of a metallic material on the semiconductor layer 41, and a passivation layer 46 is formed of an insulating material on an entire surface of the substrate 30 having the source and drain electrodes 42 and 44. At this time, in order to improve contact between the semiconductor layer 41 and the passivation layer 46, the passivation layer 46 is made of an inorganic insulating material including silicon nitride (SiNx) and silicon oxide (SiOx).
In FIG. 3D, a photosensitive layer 50 is formed of a photosensitive material on the passivation layer 46. The photosensitive material is selected from an organic material such as acrylic resin. This step includes forming an uneven pattern of squares (not shown) in a surface portion of the photosensitive layer 50 and forming the first uneven pattern 51 as a hemispherical shape by melting at a predetermined temperature within about 350 degrees Celsius.
Next, an inorganic insulating layer 54 is formed of a transparent inorganic material on an entire surface of the substrate 30 having the first uneven pattern 51 of the hemispherical shape. At this time, the inorganic insulating layer 54 has a second uneven pattern 52 of a hemispherical shape corresponding to the first uneven pattern 51 of the photosensitive layer 50. The first and second uneven patterns 51 and 52 are located in the reflective portion RP.
In FIG. 3E, portions of the passivation layer 46, the photosensitive layer 50 and the inorganic insulating layer 54 that correspond to a portion of the drain electrode 44 and the transmissive portion TP are etched to form a drain contact hole 56 and a transmissive hole 58 that expose the portions of the drain electrode 44 and the transmissive portion TP, respectively. Specifically, a portion of the gate insulating layer 36 in the transmissive hole 58 may be etched due to etching rate differences between a portion of the drain contact hole 56 and a portion of the transmissive hole 58 as shown in FIG. 3E.
In FIG. 3F, a reflective layer 60 is formed of metallic materials having a high reflectance such as aluminum (Al) and silver (Ag) on the substrate 30 having the drain contact hole 56 and the transmissive hole 58. The reflective layer 60 corresponds to the reflective portion RP except portions of the drain contact hole 56 and the transmissive hole 58.
In FIG. 3G, an inorganic insulating layer 62 is formed of an inorganic insulating material on the substrate 30 having the reflective layer 60. At this time, through this step, the inorganic insulating layer 62 has holes corresponding to the drain contact hole 56 and the transmissive hole 58 that can expose the portion of the drain electrode 42 and the transmissive portion TP.
Next, a pixel electrode 64 is formed of transparent conductive materials such as indium tin oxide (ITO) on the inorganic insulating layer 62 and is connected to the drain electrode 44 via the drain contact hole 56.
As explained above, the transflective LCD device according the related art is manufactured.
However, this method of fabricating for the transflective LCD device according to the related art uses a large number of processes and thus the overall process becomes complicated. Therefore, production yield of the transflective LCD device is reduced.